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Abstract:

A display has a light source layer having control inputs for controlling
the light source layer to emit light such that the light output varies
smoothly with position in a manner determined by the control inputs. An
LCD panel or other spatial light modulator modulates light from the light
source layer. The light source layer may be thin.

Claims:

1. A light source comprising: a light-emitting layer operative to emit
light in response to an electrical potential difference being applied
across the light-emitting layer, emitted light having an intensity
dependent upon a magnitude of the potential difference; a first electrode
structure comprising a first electrically-conductive electrode on a first
face of the light-emitting layer; and a second electrode structure
comprising a layer of a potential-distributing material having an
electrical resistance on a second face of the light-emitting layer and an
array of control points in electrical contact with the layer of
potential-distributing material at locations spaced apart over the second
face of the light-emitting layer.

2. A light source according to claim 1 comprising a power supply having a
plurality of independently-controllable outputs, the outputs each
connected to a corresponding one of the control points.

6. A light source according to claim 1 wherein the light-emitting layer
comprises an electrofluorescent material.

7. A light source according to claim 1 wherein the control points are
arranged in a triangular grid.

8. A light source according to claim 1 wherein the control points are
arranged in a rectangular grid.

9. A light source according to claim 1 wherein the control points have a
non-uniform spatial density.

10. A light source according to claim 9 wherein the control points are
concentrated more densely in a central region of the light-emitting layer
and less densely in a peripheral region of the light-emitting layer.

11. A light source according to claim 1 wherein the first electrode is
substantially transparent to the emitted light.

12. A light source according to claim 1 wherein the control points
comprise metallic pads in contact with the potential-distributing layer.

13. A light source according to claim 1 wherein the
potential-distributing layer comprises a doped semiconductor.

14. A light source according to claim 1 wherein the
potential-distributing layer comprises an electrical resistivity that
varies with position on the potential-distributing layer.

15. A light source according to claim 1 comprising optically absorbing
spots on the first surface of the light emitting layer at locations
corresponding to the control points.

16. A light source according to claim 15 wherein the optically absorbing
spots have optical densities that drop off with distance from the control
points.

17. A light source according to claim 1 wherein the light-emitting layer
is operable to emit white light.

18. A light source comprising: a light-emitting layer operative to emit
light in response to an electrical potential difference being applied
across the light-emitting layer, a plurality of control inputs, each of
the control inputs connected to control the potential difference at a
corresponding location on the light-emitting layer; control distribution
means for applying a smoothly spatially varying potential difference at
positions on the light-emitting layer between the locations corresponding
to the control inputs.

19. A light source according to claim 18 wherein the control distribution
means comprises a layer of a potential-distributing material.

20. A light source according to claim 18 wherein the control distribution
means comprises a resistor network.

21. A light source according to claim 18 wherein the control distribution
means comprises a plurality of interpolation circuits.

22. A display comprising: a light source comprising a plurality of
control inputs; and a spatial light modulator illuminated by the light
source; wherein: the control inputs correspond to spots on the light
source, the spatial light modulator comprises a plurality of pixels, each
illuminated by a different area of the light source, and the illumination
provided by each of the different areas of the light source is a function
of the position of the area relative to positions of the spots and of
signals applied to the control inputs.

23. A display according to claim 22 wherein the spots are arranged in a
rectangular array.

24. A display according to claim 23 wherein the rectangular array is a
square array.

25. A display according to claim 22 wherein the light source is
coextensive with the spatial light modulator.

26. A display according to claim 25 wherein the light source extends
parallel to the spatial light modulator.

27. A display according to claim 26 wherein the light source and spatial
light modulator are both substantially planar.

28. A display according to claim 26 wherein the light source and spatial
light modulator are both curved.

29. A display according to claim 26 wherein the light source is against a
rear face of the spatial light modulator.

32. A display according to claim 22 comprising a controller operative to
apply a first set of signals to the control inputs of the light source
and a second set of signals to control pixels of the spatial light
modulator.

33. A display according to claim 32 wherein the controller is configured
to generate each of the first and second sets of signals based upon image
data.

34. A display according to claim 33 wherein the controller is configured
to generate the first set of signals by an algorithm comprising at least
one of low-pass filtering and downsampling the image data.

35. A display according to claim 33 wherein the controller comprises:
means for generating the first set of signals from the image data; means
for estimating a light output of the light source at each of the areas;
means for generating the second set of signals from the image data and
estimated light outputs.

36. A display according to claim 33 wherein the controller comprises: a
image processor connected to receive the image data and generate the
first set of signals based on the image data; a light field estimator
connected to receive the first set of signals and to generate an estimate
of the light field that would be produced by the light source layer in
response to the first set of signals; and a computation unit connected to
receive the image data and the estimated light field and to generate the
second set of signals based on the image data and the estimated light
field.

37. A display according to claim 36 wherein the estimate of the light
field comprises a two-dimensional map indicating light intensity as a
function of position on the light source.

38. A display according to claim 36 wherein the computation unit performs
a calculation which comprises dividing an intensity value represented by
the image data for a particular pixel by a value of the estimated light
field corresponding to the area of the light source corresponding to the
pixel.

39. A display according to claim 36 wherein the light field estimator is
operative to: based on the first set of signals, determine an electrical
potential as a function fo position on the light source; and, based on a
function relating light output to applied electrical potential, estimate
light outputs for positions on the light source.

40. A display according to claim 36 wherein the illumination provided by
the light source varies smoothly in a manner given by the equation:
l x ≦ L a - L b x a - x b × ξ
##EQU00002## where l is the light intensity; x is a measure of
position, La and Lb are the light intensities at two adjacent
control points on the light source; xa and xb are the locations
of the control points and ξ is a parameter having a value in the range
of 1 to 11/2.

41. A display according to claim 22 wherein the light source comprises a
plurality of light-emitting layers, each coextensive with the spatial
light modulator, with a second of the light emitting layers being between
a first one of the light emitting layers and the spatial light modulator.

42. A display according to claim 41 wherein the first and second
light-emitting layers are operable to emit light having distinct spectral
characteristics and the second light-emitting layer is transparent to
light of at least some wavelengths included in the spectral
characteristics of the first light-emitting layer.

45. A display according to claim 22 wherein a thickness measured between
a front face of the spatial light modulator and a rear face of the light
source is 2 cm or less.

46. A display according to claim 22 wherein the light source has 50 to
5000 control inputs.

47. A display according to claim 22 wherein a ratio of control spots of
the light source to pixels of the spatial light modulator is in the range
of 1:200 to 1:40,000.

48. A display according to claim 22 wherein the spatial light modulator
comprises 1 million or more pixels and the number of control spots is ten
thousand or fewer

49. A display comprising: a light source comprising a layer of a material
that emits light in response to applied electrical field, the layer
extending in two dimensions, one or more power supplies operable to
deliver individually-controllable electrical potentials to a plurality of
spaced-apart locations on the light source, and a non-insulating material
extending between the locations such that electrical potentials at
positions on the light source on a path between two adjacent ones of the
spaced apart locations change smoothly with position along the path; and
a spatial light modulator illuminated by the light source, the spatial
light modulator comprising a plurality of pixels, each pixel illuminated
by a different area of the light source.

50. A display comprising: a substantially continuous
two-dimensionally-extending layer of a material that emits light in
response to an applied electrical field; means for applying an electrical
field across the layer, the electrical field having a magnitude that
varies smoothly with position on the layer; and a spatial light modulator
comprising an array of pixels wherein the layer is parallel to and in
aligned relationship to the spatial light modulator.

51. A method for displaying an image specified by image data, the method
comprising: based on the image data, generating first control signals to
be applied to a plurality of spaced apart control points of a light
source; estimating a light output of the light source at locations at and
between the control points; based on the estimated light output and the
image data generating control signals for pixels of a spatial light
modulator; applying the first control signals to the control points of
the light source and thereby causing the light source to emit light at
and between the control points and applying the second control signals to
control the pixels of the spatial light modulator.

52. A method according to claim 51 wherein estimating the light output of
the light source comprises modeling an electrical potential distribution
over the light source resulting from application of the first control
signals and establishing an estimated light output at points of a
two-dimensional map of the light source as a function of the electrical
potential corresponding to the points.

53. A method for generating illumination that varies smoothly over a
two-dimensional surface of a light source, the method comprising:
providing a substantially continuous two-dimensionally-extending layer of
a material that emits light in response to an applied electrical field;
and, applying an electrical field across the layer, the electrical field
having a magnitude that varies smoothly with position on the layer.

54. A method for generating light having an intensity that varies
smoothly with position, the method comprising: providing a light emitting
material of a type that emits light at a point in response to the
application of a control signal at the point; generating a first
plurality of control signals each associated with a corresponding point
of a first set of points on the light-emitting material; applying each of
the first plurality of control signals to the corresponding first point
on the light-emitting material; generating a second set of control
signals associated with a corresponding second point on the
light-emitting material, the second points not including the points of
the first set, by connecting the first plurality of control signals as
inputs to an analog circuit and applying each of the second plurality of
control signals to the corresponding second point on the light-emitting
material.

55. A method according to claim 54 wherein the analog circuit comprises a
voltage divider.

56. A method according to claim 54 wherein the analog circuit comprises a
resistor network.

58. A method according to claim 54 wherein the analog circuit comprises
an array of interpolation circuits.

59. A method according to claim 54 wherein the analog circuit comprises a
continuous layer of an electrically resistive material.

60. A method according to claim 59 wherein the electrically-resistive
material has a sheet resistance of 10.sup.12 Ω/square or less.

61. A method according to claim 59 wherein the electrically-resistive
material has a sheet resistance in the range of 10.sup.2 to 10.sup.7
Ω/square.

62. A method according to claim 54 wherein the points of the first set of
points are arranged in a regular array on the light-emitting material.

63. A method according to claim 54 wherein the second plurality of points
form a continuous region that surrounds points of the first plurality of
points.

64. A light source for generating light having an intensity that varies
smoothly with position, the light source comprising: a layer of a
light-emitting material extending in two dimensions and operative to emit
light at a point in response to the application of a control signal at
the point; a plurality of first control inputs each
electrically-connected to apply a control signal at a corresponding point
of a first set of points on the light-emitting material; an analog
circuit having inputs connected to the first control outputs and outputs
electrically connected to deliver control signals at corresponding second
points on the light-emitting material, the second points not including
the points of the first set.

65. A display comprising: a source of image data defining one or more
images to be displayed; a logic unit configured to process the image data
to obtain first driving signals corresponding to spaced-apart first
locations on a two-dimensional light source; an analog circuit connected
to receive the first driving signals as inputs and operative to produce
second driving signals corresponding to second locations on the light
source outside of the first locations; the light source connected to be
controlled by the first and second driving signals; and a spatial light
modulator comprising an array of pixels and arranged to be illuminated by
light emitted by the light source.

66. A display comprising: a source of image data defining one or more
images to be displayed; a logic unit configured to process the image data
to obtain first signals corresponding to desired light intensity at
spaced-apart first locations on a two-dimensional light source; an analog
circuit connected to receive the first signals as inputs and operative to
produce a plurality of driving signals, wherein a number of the driving
signals exceeds a number of the first signals; the light source connected
to be controlled at least in part by the driving signals; and a spatial
light modulator comprising an array of pixels and arranged to be
illuminated by light emitted by the light source.

67. Methods comprising any new and inventive, step, act, combination of
steps and/or acts or sub-combination of steps and/or acts as described or
depicted herein.

68. Apparatus comprising any new and inventive feature, combination of
features or sub-combination of features as described or depicted herein.

[0002] This invention relates generally to displays. Some non-limiting
examples of displays are televisions, home cinema displays, computer
displays, commercial displays, stadium displays, electronic billboards
and the like. The invention relates to displays of the type that have
spatially variable backlights and to backlights suitable for such
displays.

BACKGROUND

[0003] Some displays have a spatial light modulator, such as a LCD panel,
illuminated by a backlight. Light from the backlight interacts with the
spatial light modulator which spatially modulates the light so as to
present images to a viewer. The images may be still images or video
images for example. In some such displays, the backlight has different
areas that are separately controllable so that the intensity of light
emitted by the backlight can be made to vary in a desired way over the
spatial light modulator. This can provide improved images. Examples of
displays that have spatially variable backlights are described in the
following patent publications:

[0004] There is consumer demand for displays that are thin front-to-back.
Such displays can be more easily accommodated in some locations than
thicker displays and are also less bulky in appearance than thicker
displays.

SUMMARY

[0005] This invention has a range of aspects. Some different aspects
provide: [0006] displays which may be, for example, computer displays,
televisions, video monitors, home cinema displays, commercial displays,
industrial displays, electronic billboards or the like; [0007] backlights
usable in displays; [0008] controllers for displays; and, [0009] methods
for operating backlights and displays.

[0010] In addition to the exemplary aspects and embodiments described
above, further aspects and embodiments will become apparent by reference
to the drawings and by study of the following detailed descriptions.

[0022]FIG. 7 shows schematically an electrical network in a backlight
according to an example embodiment of the invention.

[0023] FIGS. 8A and 8B illustrate a variation in electrical field with
position along a light emitter for various control inputs.

[0024]FIG. 9 is a schematic view of a backlight according to an example
embodiment having an absorbing layer that is densest at locations
corresponding to control points.

[0025]FIG. 10 is a Schematic view of a color display according to an
example embodiment.

[0026]FIG. 10A is an enlarged schematic view of the portion 10A of the
light source of the display of FIG. 10.

[0027]FIG. 11 is a schematic depiction of a display according to another
embodiment.

DESCRIPTION

[0028] Throughout the following description specific details are set forth
in order to provide a more thorough understanding to persons skilled in
the art. However, well known elements may not have been shown or
described in detail to avoid unnecessarily obscuring the disclosure.
Accordingly, the description and drawings are to be regarded in an
illustrative, rather than a restrictive, sense.

[0029]FIG. 1 shows a display 10 according to the prior art. Display 10
has a backlight 12 which illuminates a spatial light modulator 14.
Spatial light modulator 14 comprises an array of pixels 15 which can be
controlled to pass varying amounts of the light incident on them to a
viewing area. In the illustrated display, the spatial light modulator is
of a transmissive type. Spatial light modulator 14 comprises an LCD
panel, for example.

[0031] It is generally desirable that the illumination of spatial light
modulator 14 vary smoothly from place to place to avoid visible
artifacts. In the display shown in FIG. 1, this is achieved by ensuring
that the light from different neighboring light emitting elements 16
overlaps at spatial light modulator 14. This, in turn, is achieved by
providing a space D between light emitting elements 16 and spatial light
modulator 14.

[0032] A controller 18 controls the intensity of light emitted by light
emitting elements 16 and also the transmissivity of pixels 15 of spatial
light modulator 14 in response to image data received at an input 19.

[0033]FIG. 2A shows a point spread function 20 of an individual light
emitting element 16 of the display of FIG. 1 as well as point spread
functions 20A and 20B for neighboring light emitting elements 16. The
point spread functions vary smoothly across spatial light modulator 14.
Curve 21 shows the sum of the point spread functions as a function of
position. Curve 21 also indicates the variation of light intensity with
position on spatial light modulator 14 for the case that all of light
emitters 16 are driven to emit light of equal intensities. Curve 21 may
be made to be quite uniform by appropriate selection of the spacing
between light emitters 16, the point spread functions of light emitters
16 and the distance D.

[0034] FIG. 2B illustrates a situation in which four light emitters 16 at
locations x1 through x4 are driven at different intensity
levels. Curves 20-1 through 20-4 indicate the amount of light emitted by
each of the light emitters as a function of position on spatial light
modulator 14. Curve 22 is the sum of the light emitted by the light
emitters 16 on spatial light modulator 14. It can be seen that by
appropriately controlling the intensity of light emitted by light
emitters 16 the intensity of light with which spatial light modulator 14
is illuminated can be made to vary fairly smoothly from point to point on
spatial light modulator 14.

[0035] A disadvantage of display 10 is that the distance D required for an
optimal distribution of light on spatial light modulator 14 from light
emitters 16 may be sufficiently large that the display is thicker than
might otherwise be desired.

[0036]FIG. 3 illustrates a display 30 according to an example embodiment
of the invention in which a distance d between a light source layer 32
and a transmissive spatial light modulator 14 having controllable pixels
15 may be fairly small. In some embodiments the light source layer 32 may
be directly against or integrated with spatial light modulator 14.
Display 30 comprises a controller 34 that generates control signals 35
that control light source layer 32 to emit light having an intensity that
varies spatially over the area of spatial light modulator 14. Controller
34 also generates control signals 36 that control the pixels 15 of
spatial light modulator 14. Controller 34 receives image data at an input
37 and, based on the image data, generates control signals 35 and 36 to
cause a viewer V to see an image according to the image data.

[0037]FIG. 4 is a functional block diagram of a controller 34 that may be
used in the display of FIG. 3. The components of controller 34 may
comprise one or more of: [0038] one or more data processors (which may
comprise general purpose processors, digital signal processors or
graphics processors, for example, executing software or firmware
instructions that cause the data processors to operate as described
below; [0039] hard-wired logic circuits (which may be, for example,
provided in one or more application-specific integrated circuits
(ASICs)); [0040] configurable logic hardware such as field-programmable
gate arrays (FPGAs) configured to provide signal processing paths that
provide outputs as described below; [0041] etc.

[0042] An image processor 40 receives image data from input 37 and
generates signals 41 that control light source driver circuits 42 to
cause light source layer 32 to generate light having a desired spatial
variation in intensity. Driving signals 41 are also supplied to a light
field estimator 44 which produces an estimate 47 of the light field that
would be produced by light source layer 32 in response to the driving
signals 41. Light field estimator 44 produces light field estimate 47
based in part on light source response characteristics 45. Light source
response characteristics 45 may, for example, comprise functions or
parameters that are in a data store accessible to light field estimator
44. Light field estimate 47 may comprise a two-dimensional map indicating
light intensity as a function of position on light source layer 32 for a
given set of signals 41.

[0043] In some embodiments, image processor 40 derives signals 41 by a
process that generates a lower-resolution version of the image data. This
may be done, for example, by a process that involves one or more of
low-pass filtering; downsampling; and/or taking local weighted averages
of pixel values specified in the image data. The lower resolution version
of the image data may be passed through a scaling function to generate
signals 41. Advantageously, the application of signals 41 to light source
layer 32 results in the emission of light that, at every pixel of spatial
light modulator 14, is somewhat more intense than is required for that
pixel by the image data. The pixels of spatial light modulator 14 can
then be operated to attenuate the light to have an intensity at each
pixel as specified by the image data.

[0044] In some embodiments, light field estimation comprises, based on
control inputs estimated to correspond to control signals 41, estimating
electrical potentials corresponding to positions on light source layer 32
and, based on a function relating light output for each area of light
source layer 32 to applied electrical potential (or electrical field)
estimating light outputs for the positions on light source layer 32.
These steps may be performed at a resolution lower than that of modulator
14. If there is an optical path between light source layer 32 and
modulator 14 that affects the light emitted by light source layer 32 then
light field estimation may comprise applying a point spread function or
other model of the effect of the optical path on the light outputs
determined above.

[0045] A computation unit 48 receives image data and the estimated light
field 47 and generates driving values 49 which control the transmission
of light by pixels 15 by way of modulator driver circuits 50. In some
embodiments, computation unit 48 performs a calculation which comprises
dividing an intensity value represented by the image data for a
particular location by a value of the estimated light field corresponding
to that location. Corrections may be applied to take into account a
response of modulator driver circuits and/or spatial light modulator 14
to driving signals 49.

[0046] Advantageously light source layer 32 may have significantly fewer
control inputs than spatial light modulator 14. In spatial light
modulator 14, each pixel 15 can be individually addressable. Light source
layer 32 is controllable in a coarser resolution. However, light source
layer 32 is constructed such that its light output varies with a desired
smoothness.

[0047] In some embodiments, this smoothness is expressed by the equation:

l x ≦ L a - L b x a - x b
× ξ ##EQU00001##

where l is the light intensity; La and Lb are the light
intensities at two adjacent control points on light source layer 32;
xa and xb are the locations of the control points. The
difference |xa-xb| is equal to a resolution by which light
source layer 32 is controlled. ξ is a parameter having a value in the
range of 1.0 to 1.5.

[0048] FIGS. 5A and 5B show two example constructions for light source
layer 32. Light source layer 60 shown in FIG. 5A has a light generating
layer 62 located between an optically transparent front electrode 63 and
a rear electrode structure 64. Light generating layer 62 emits light
having an intensity determined by an electrical field across light
generating layer 62. Electrode structure 64 comprises a number of control
points 65 connected to driving circuits by suitable conductors 66. The
driving circuits (designated by C1, C2, C3 in the illustrated embodiment)
can control the electrical potentials applied to different control points
65. In some embodiments the electrical potentials applied by the driving
circuits are relatively low, for example, 15 volts or lower. Higher
voltages may be applied in other embodiments.

[0049] It is not mandatory that control points 65 be point-like. In some
embodiments, control points 65 comprise electrically-conductive pads. The
pads are relatively large compared to pixels of a spatial light modulator
in some embodiments. The pads may be but are not necessarily round. The
pads may have rounded corners.

[0050] Light source layer 60 may comprise, for example, organic light
emitting diode (OLED) layers, substrates coated with or incorporating
phosphors, white Field Emissive Display (FED) layers, phosphor-coated
plates, electrofluorescent materials, and the like. In general, any
electro-luminescent technology may be applied in light source layer 60.
These technologies operate on the common principle of converting
electrical energy into photon (light) emission. Typically electrical
potential across a thin layer or a suitable material results in light
emission. The magnitude of the light emission can be approximately
proportional to the strength of the electrical field applied across the
thin layer material (and the corresponding current flow).

[0051] A layer of a potential-distributing material 67 is in contact with
and extends between control points 65. The potential-distributing
material may comprise a material that is electrically conducting but has
electrical resistance such that the electrical potential varies smoothly
as one moves between the control points along a path in the
potential-distributing material. In some embodiments
potential-distributing material 67 may comprise a weak electrical
conductor, for example a suitable conducting polymer or other resistive
film.

[0052] The degree of electrical conductivity of the layer of
potential-distributing material 67 may be chosen depending upon the
amount of electrical current needed (if any) to actuate light source
layer 60. Where light source layer 60 draws only a low or very low
current then potential-distributing material 67 may comprise a
nearly-insulating dielectric material, for example (although a material
having greater electrical conductivity could also be used). Where light
source layer 60 is of a type that draws greater amounts of electrical
current (for example a strongly emissive layer such as a layer of OLEDs)
then potential-distributing material 67 advantageously has a somewhat
greater electrical conductivity. In some embodiments the
potential-distributing material may have a sheet resistance of 1012
Ω/square or less. In some embodiments the potential-distributing
material has a sheet resistance of 107 Ω/square or less. In
some embodiments the potential-distributing material has a sheet
resistance in the range of 102 or 103 to 107
Ω/square.

[0053] If all of control points 65 are maintained at the same electrical
potential by the control circuits then the electric field across all
portions of light generating layer 62 is fairly uniform with the result
that the light emitted by light source layer 60 is fairly spatially
uniform.

[0054] On the other hand, if different ones of control points 65 are
maintained at different electrical potentials then the electrical
potential will vary from place to place on electrode structure 64. This
variation of electrical potential will, in general, be smooth because of
the presence of potential-distributing material 67. The intensity of
light emitted by light emitting layer 60 will therefore vary from
location to location in a smooth manner with the overall variation in
light intensity determined by the combination of electrical potentials
that are applied to control points 65.

[0055] Control points 65 may, for example, be arranged in a regular array,
such as a grid, a hexagonal or triangular array, a rectangular array or
the like. It is not mandatory that the control points have a uniform
spatial density or that all neighboring control points be equidistant
from one another.

[0056] Preferably potential-distributing layer 67 has a reasonably high
electrical resistivity so that when different control points 65 are
maintained at different electrical potentials, the electrical current
flowing between different ones of control points 65 through
potential-distributing layer 67 is fairly small and does not dissipate
significant amounts of energy so as to cause potential-distributing layer
67 or light generating layer 62 to overheat.

[0057] In displays according to some embodiments, there are in the range
of 50 to 5000 control points. In some embodiments, a ratio of control
points to pixels is in the range of 1:200 to 1:40,000. In some
embodiments the display comprises 1 million or more pixels whereas the
number of control points is a few thousand or less.

[0058]FIG. 5B shows a light source layer 70 according to an alternative
embodiment. Light source layer 70 has a light generating layer 72 which
is divided into an array of pixels 73. Each pixel 73 generates light
having an intensity determined by an electrical field between a
transparent front electrode 74 and a control electrode 75. In the
illustrated embodiment, transparent front electrode 74 is common to all
of the pixels. This is not mandatory. Control electrodes 75 are not each
individually controlled in this embodiment. Instead, the potential on
each of control electrode 75 is determined by the potential at a
corresponding node of a resistor network 76. Driving circuits (designated
by C1, C2 in the illustrated embodiment) are connected to some but not
all nodes on resistor network 76. The potential at such control nodes is
determined by the driving signals applied by the driving circuits. The
potential on other nodes is determined by the potential drop over the
various resistors 77 in resistor network 76. Resistors 77 do not need to
be discrete components. Resistors 77 may be fabricated in or on a
substrate by any suitable patterning technique, for example. It can be
appreciated that the illumination layers 60 and 70 illustrated in FIGS.
5A and 5B can be controlled to emit light in such a manner that the light
intensity varies with position on the light emitting layer with
relatively few control inputs.

[0059] In some embodiments, a light emitting layer incorporates active
electronics. For example, FIG. 5C shows an embodiment wherein the light
source layer 78 comprises an array of small, closely-spaced light sources
78A. Light sources 78A may, for example, comprise light emitting
semiconductor junctions such as light emitting diodes or organic light
emitting diodes (OLEDs) or the like. Some but not all of light sources
78A are independently controllable. The driving values of the remaining
light sources are interpolated from the driving values of the
controllable light sources by interpolation circuits 79. For example, the
illustrated embodiment shows a 10 by 10 array of light sources having
control points (C1,1, C10,1, C1,10, C10,10) at its
four corners. The driving values at control points C1,1, C10,1,
C1,10, C10,10 are independently controllable. The driving
values of each of the other light sources within the array are determined
by an interpolation circuit 79, as is illustrated for a single light
source 78A in FIG. 5C. The illustrated interpolation circuit 79 takes as
inputs the driving values of control points C1,1, C10,1,
C1,10, C10,10 and outputs a driving value for corresponding
light source 78A. The output of a particular interpolation circuit 79 may
be determined by multiplying the driving values at each input control
point by a corresponding fixed parameter. The parameters are proportional
to the relative distances between the input control points and the given
light source. Parameters of interpolation circuits 79 may be set
differently for different light sources. When suitable control signals
are applied to the control points, the individual light emitting diodes
emit light that varies smoothly over the array of light emitters.

[0060]FIG. 6 illustrates a light emitting layer 80 according to another
embodiment. Light emitting layer 80 has an array of electrically
conducting pads 81 on its rear surface 81A. As shown in FIG. 6A, each pad
81 is connected to a control line 82 in any suitable manner. A layer 83
of a weakly electrically conducting material is applied over control
points 81. A light generating material 84A is located between rear
surface 81A of light emitting layer 80 and an optically transparent front
electrode 84B. Light generating material 84A emits light having an
intensity determined by an electrical field across light generating
material 84A. The intensity of light emitted by light emitting layer 80
will vary from location to location in a smooth manner based on the
electrical potentials that are applied to pads 81.

[0061]FIG. 7 illustrates a resistor array 85 having control points at its
corners. In the illustrated embodiment, the control points divide the
resistor array into 5×5 arrays of nodes. The control points are
therefore at nodes Cij, ci,j+5, ci+5; . . . etc. A
potential at each node is a function of the potentials applied to the
control points. The potentials at the different nodes may be applied to
control a light output for a corresponding area of a light emitting
layer.

[0062] FIGS. 8A and 8B illustrate light emission from a light emitter
according to an example embodiment. In each case, the locations of
control points are indicated by x1, x2 and x3. FIG. 8A
illustrates a situation in which an equal potential is applied to each of
the control points. It can be seen that the curve 90 which indicates the
light emission across the light emitting layer is relatively constant.
FIG. 8B illustrates a situation in which a greater potential is applied
to control point x1 than is supplied to control points x2 and
x3. It can be seen that the light emission indicated by curve 90
varies smoothly from a higher level at control point x1 to lower
values corresponding to the electrical potentials at control points
x2 and x3.

[0063] In some embodiments, an optically absorbing layer is applied to the
front surface of light emitting layer 32 to reduce the intensity of light
emitted at brighter regions (e.g. regions corresponding to control
points) so as to permit the light output of the light emitting layer to
be set to be completely uniform. FIG. 9 shows an example embodiment
wherein an absorbing layer 94 has a greater optical density (i.e. absorbs
more light) in areas at or near to control points 95. The optical density
of the absorbing layer 94 drops off with distance from the control
points. The optical density most conveniently drops off smoothly with
distance from control points 95. In alternative embodiments, the known
light emission from the light emitting layer is compensated for in image
processing which appropriately sets pixels of the spatial light modulator
based upon the light emitted by the light emitting layer.

[0064] In some embodiments, the light emitted by light source layer 62 is
monochrome. In other embodiments, the emitted light spans a broader color
gamut. For example, the emitted light may comprise broadband light or a
mixture of light having different spectra. In some specific example
embodiments light source layer 62 emits light that is white or can be
filtered to yield white light. White light may, for example, be generated
by: [0065] providing a mixture of broadband light emitters in light
source layer 62. The broadband light emitters may comprise, for example,
blue and yellow broadband phosphors. Such phosphors are used in some
white LEDs. [0066] providing a mixture of narrow-band light sources in
light source layer 62. The narrow-band light sources may comprise, for
example, sources of red, green and blue light. [0067] some combination
thereof. [0068] etc.

[0069] In some embodiments light from two or more light source layers 62
is combined to provide illumination of a spatial light modulator 14. In
some embodiments, the different light source layers 62 are constructed to
provide light having spectral characteristics. For example, a color
display may comprise separate red-, green- and blue-emitting light source
layers 62.

[0070]FIG. 10 shows a display 100 according to an example embodiment.
Display 100 has a color spatial light modulator 102 illuminated by a
backlight comprising first, second and third light emitters 104A, 104B
and 104C (collectively light emitters 104). Light-emitters 104B and 104C
are essentially transparent to light emitted by light emitter 104A. Light
emitter 104C is essentially transparent to light emitted by light
emitters 104A and 104B. As shown in FIG. 10A, each light emitter 104 may
comprise a light-emitting layer 108 sandwiched between a common electrode
109 and a control layer 110. Control layer 110 is constructed according
to an embodiment such as those described herein which permits the amount
of light emitted to be controllably varied smoothly from location to
location in response to a relatively small number of control inputs. The
electrodes and control layers may comprise optically transparent
materials that are electrically conducting, such as indium tin oxide. The
thickness and doping of the control layer may be adjusted to provide
desirable resistivity characteristics.

[0071] In the embodiment illustrated in FIG. 10A, the upper two
light-emitting layers 108 (as seen in the Figure) share one common
electrode 109. This is not mandatory. Each light-emitting layer 108 could
have a separate common electrode 109.

[0072] In display 100, each light emitter 104 may be separately
controlled. In the illustrated embodiment, a three-channel controller 112
receives image data 115 defining color images. Controller 112 generates
sets of control signals 106A, 106B and 106C which control driving
circuits for light emitters 104A, 104B and 104C respectively. Controller
112 estimates the resulting amount of light of each color at pixels of
spatial light modulator 102. This estimation is based on properties 107A,
107B and 107C of the light emitters 104A, 104B and 104C respectively.
Controller 112 generates control signals 114 for the pixels of spatial
light modulator 102. The control signals are generated from the estimated
amounts of light and the image data. In an alternative embodiment, the
display of different colors is time multiplexed. In such embodiments,
spatial light modulator 102 may be a monochrome spatial light modulator.

[0073]FIG. 11 shows a display 200 according to another example
embodiment. Display 200 has a controller 210 which receives or accesses
image data 212. Controller 210 is configured to generate from image data
212 a plurality of first output signals 214 that are impressed on a
corresponding plurality of output lines 215. Output lines 215 are
supplied as inputs to a circuit 217 that has a plurality of output lines
220 that can carry driving signals 222. Output lines 220 are connected to
control the intensity of illumination provided by areas of a light source
225. Circuit 217 operates to cause light source 225 to emit light such
that the intensity of the emitted light varies smoothly over an emitting
surface of light source 225. The combination of controller 210 and
circuit 217 results in areas of light source 225 corresponding to
brighter areas of an image specified by image data 212 emitting light
that is more intense while areas of light source 225 corresponding to
dimmer areas of the image emit light that is less intense.

[0074] Controller 220 also generates control signals 227 for a spatial
light modulator 229. Control signals 227 control pixels of spatial light
modulator 229 by way of a suitable driving circuit 230. Controller 230
may, for example, have a construction like that of controller 34 which is
described above.

[0075] In embodiments having a potential-distributing layer, it is not
mandatory that the potential-distributing layer be uniform in
resistivity. In some embodiments the potential-distributing layer is
variably doped, has a variable thickness or is otherwise spatially varied
to produce desirable electrical field characteristics.

[0076] An alternative way to smoothly control light output based on a
relatively small number of control inputs is to provide a light absorber,
such as a LCD, controlled as described above. In such embodiments, the
light transmission at different spatial locations of the LCD is a
function of the electrical potential at those locations.

[0077] While a number of exemplary aspects and embodiments have been
discussed above, those of skill in the art will recognize certain
modifications, permutations, additions and sub-combinations thereof. It
is therefore intended that the following appended claims and claims
hereafter introduced are interpreted to include all such modifications,
permutations, additions and sub-combinations as are within their true
spirit and scope.